Show that if a straight line is perpendicular to one of the two or more parallel lines, then it is also perpendicular to the remaining lines.

Let GH intersect AB and CD at L and M respectively. Since GH is perpendicular to AB. We have ∠GLA = 90°. GH is also perpendicular to CD. Thus ∠GMC = 90° . we get ∠GLA = ∠GMC = 90°. Thus the lines are parallel. And angles are corresponding angle. Since CD is also parallel with EF. Hence ∠GNE = 90°. Hence it is perpendicular to all other lines in the same way.